This invention relates to wood flooring and more particularly to an improved, dimensionally stable wood flooring which is highly resistant to deterioration because of variations in humidity and temperature.
It is well known that wood flooring fillets expand and contract significantly when exposed to changes in temperature and humidity. This dimensional instability has been a serious problem in wood floors, especially those in which the wood strips or fillets are not secured to one another by means of a backing material, but rather are adhered directly to a subfloor. Such a floor is subject to buckling if inadequate space is provided between the fillets so that upon expansion they press unduly against one another. To prevent buckling, some prior floors employed relatively large gaps between adjacent fillets. Not only are large gaps unsightly, but they can become filled with dirt and grit, effectively diminishing the available expansion space. In other floors, especially those covering large areas, adjacent tiles made up of a plurality of fillets have been laid with their grains running in alternate directions. Because woods expand and contract by differing amounts in different directions with respect to grain orientation, such a parquet arrangement limits dimensional changes across the gaps separating contiguous tiles, thereby reducing the likelihood of buckling.
One approach to solving the dimensional instability problem has been to fill the gaps with a flexible bonding material which has sufficient compressibility to accommodate the maximum change in gap width. See, for example, U.S. Pat. No. 3,365,850 in which the preferred bonding material is a blend of chloroprene synthetic rubber, esterified rosin and an antioxidant. Although this material remains flexible, it is of limited compressibility so that only a relatively small portion of the gap thickness is available for fillet expansion.
The limited compressibility and expandability of the previously used gap filling materials have several disadvantages. First, since much of the gap width cannot be utilized, the maximum amount of expansion of a fillet for a given gap width must be limited. One means of bounding expansion has been to limit the maximum width of the fillet to approximately one inch. Another means has been to orient the fillet with respect to the wood grain so that the surface adjacent to the gap is the flat grain face. It is known that dimensional changes transverse to the flat grain faces are less than for other grain orientations. A third way to control the amount of dimensional change is to use woods with inherent dimensional stability. Woods such as beech and gumwood have accordingly been avoided in the past because they are less dimensionally stable than other woods, such as oak and maple. Again, because of the limited elasticity of the previously used binding material in the gap, high shear stresses develop between fillets during expansion, requiring very rigid adhesive to prevent the fillet from breaking away from the subfloor. Each of these constraints imposed by the prior gap-filling materials adds considerably to the cost of the finished floor.
It is, therefore, an object of the present invention to provide dimensionally stable wood flooring having a highly compressible gap-filling material between the wood fillets, that is, a material which can be compressed to a small fraction of its unstressed thickness.
It is a further object of the invention to provide a gap filler that allows the use of wider fillets or planks made up of multiple fillets, and eliminates the need to alternate the grain direction of adjacent planks, especially advantageous in floors covering large open areas.
Yet a further object is a gap filler for wood flooring for which the fillet surface adjacent to a gap is a mixed or flat grain.
Still another object is a gap filler which permits wood flooring to be secured to a subfloor with a lower cost, less rigid and more tacky adhesive than before possible.
A still further object of the invention is a gap-filling material which allows the flooring to accommodate an irregular subfloor.
Other objects, features and advantages of the present invention will become apparent in what follows.